Producing all skin rayon



United States Patent PRODUCING ALL SKIN RAYON Wayne A. Sisson, Media, andByron A. Thumm, Prospect Park, Pa., assignors to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed June 29, 1955, Ser. No. 518,934

13 Claims. (Cl. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from .viscose. I

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filamens, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellucertain composition limits which will be defined hereinafter. The most readily distinguishable characteristic as compared to conventional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of such compounds as are perhaps more technically classed as polyoxyalkylene glycol ethers of triethanolamine such as, for example, the ethers of polyoxyethylene and polyoxypropylene glycols and triethanolamine. It is possible that the adducts may have polyoxyalkylene chains of different length and that the alkylene oxide units are not in all cases equally distributed in the triethanolamine derivatives. The alkylene oxide content of the ethers is, therefore, expressed as the-average number of alkylene oxide units per molecule of triethanolamine. The adducts must have sutficient water and alkali solubility to permit the required amount to be dissolved in the viscose, spinning bath or both. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic soda solution, the ethylene oxide adducts or polyoxyethylene glycol ethers of triethanolamine are preferred. Accordingly, the invention will be illustrated specifically by reference to ethylene oxide adducts.

The average alkylene oxide content of the adducts or others should be at least about 9 alkylene oxide units per molecule of triethanolamine and, depending upon the specific alkylene oxide, may be as high as 100 or more units. The upper limit is determined by the solubility and stability characteristics of the adducts. Thus, the

' upper limit in the case of propylene oxide adduct is lower lose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarcation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stilt.

It has now been discovered that the presence of small amounts of alkylene oxide adducts of triethanolamine in the viscose, in the spinning bath, or in both the viscose and the bath results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of adduct is maintained within certain limits and the composition of the spinning bath is maintained within than the upper limit for the ethylene oxide adducts. For practical and commercial purposes, it is uneconomic to employ adducts having alkylene oxide contents approaching the upper limit because these higher cost substances are not more effective than the lower and intermediate substances. Thus, in the case of the. ethylene oxide adducts, it is preferred to employ adducts containing between about 9 and about 30 ethylene oxide units per molecule of triethanolamine.

Where the adduct is to be added to the viscose, the amount which is incorporated in viscose must be at least about 0.5% by weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from about 1% to 2%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts afiect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined Wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 6% to about 10% cellulose, the particular sourceof the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The. modified viscose, that is, a viscose containing the small amount of alkylene oxide adduct of triethanolamine, may have a sodium chloride salt test above about 7 and preferably above about 9 at the time of spinning or extrusion. The term salt test as used herein refers to the conventional sodium chloride salt test.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of these adducts in the viscose or in the spinning bath combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically, and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about to about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and' from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 0, preferably between about 45 C. and about 70 C. As is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is Preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufiiciently rapid to form a filament having a skin and core.

There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufliciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a.7% cellulose, 6% caustic-viscose and containing these adducts lies between about 6% and about 7.8%. Lesser amounts of acid may be employed. The acid concentration may be increased as the amount of the adduct is increased and also as the salt test of the viscose is increased. Thereis an upper limit, however, for the acid concentration based upon the amount of adduct and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of adduct is increased beyond about 4% while other conditions are maintained constant. A lowering of the amount of the adduct in the viscose, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. The maximum concentration 'of acid which is permissible for the production of all skin products is about 8.5%.

The presence of the alkylene oxide adducts of triethanolamine in the viscose retards the coagulation and, therefore, the amount of adduct employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a vi scose as above and at a spinning speed of about 50 meters per minute, the adduct is employed in amounts I 4 1%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath fora period sufiicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufiicient so that the filaments will not adhere to each other as they are brought together and withdrawn from, the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removalfrom the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot Water or a dilute acid solution and may be stretched from about 70% to 120%, preferably between 80% and 100%. Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to'about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the vention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss within the lower portionof the range, for example, about of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the adducts have superior abrasion and fatigue resistance characteristics and have a high flex-life as compared to normal regenerated cellulose filaments. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

Like improvements in the characteristics and properties of the products are also obtained by incorporation of the described alkylene oxide adducts of triethanolamine in the spinning bath in place of adding it to the viscose. It is essential, however, that the composition of the spinning bath, particularly the acid concentration, be maintained within the limits set forth hereinbefore. In order to produce products consisting of all skin, the amount of the adduct dissolved in the spinning bath must be at least about 0.03% by weight and may be as high as about 0.5% and is preferably maintainedbetween about 0.1%

5 and about 0.2%. The upper limit of the amount added to the spinning bath for commercial production is also dependent upon economic considerations since amounts exceeding about 0.2% are not more efiective in improving the properties of the products.

It is obvious that the adducts may be added to both the viscose and the spinning bath, if desired. In such instance, it is also essential to maintain the amounts of the adduct in the viscose and in the spinning bath, and the composition of the spinning bath within the stated limits. The all skin products of improved properties are obtained only when the spinning operation in the presence of these adducts is carried out within the spinning bath composition as set forth hereinbefore. It is obvious that in commercial production methods it is impractical to employ a spinning bath which does not contain the adduct. Where the adduct is present in the viscose, the adduct is leached from the viscose during spinning and is then present in the bath. Accordingly, the specific examples set forth herein are representative of commercial practice. It is to be understood, however, that from an academic standpoint all skin products can be produced by utilizing a spinning bath within the stated composition range but containing no adduct.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7.4% cellulose, about 6.3% caustic soda, and having a total carbon disulfide content of about 41% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2% hours. The cellulose xanthate was then dis solved in caustic soda solution. An additional 5% carbon disulfide was'then added to the mixer and the mass mixed for about one hour. The viscose was then allowed to ripen for about 30 hours at 18 C. In those instances where an ethylene oxide adduct of triethanolamine was incorporated in the viscose, the desired amount of adduct was added to the solution and mixed for about /2 hour before allowing the viscose to ripen.

In each instance, the viscose was extruded through a spinneret to form a 215 denier, 120 filament yarn at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. From the spinning bath the yarn was passed through a hot water bath maintained at about 95 C. and was stretched about 82% while passing through this bath. The yarn was collected in a spinning box, washed free of acid and sa ts and dried.

The specific spinning conditions and the physical properties of the yarns are set forth in the following table:

Example I II III IV V VI VII VIII Viscose:

Percent adduct 1 2 1 2 1 2 0 Salt test 10 9. 9 9. 8 9. 9 I 9. 4 9.8 10.1 10. 2

Percent H1304 7. 6 7. 5 7. 5 7. 5 7. 6 7.4 7.6 7. 5 Percent ZnSO; 7. 8 7.8 7. 9 7.9 8 8. 1 8 8 Percent P 82804 19 19 20 20 2O 20 20 19 Percent adduct 0.1 0. 1 0. l 0.1 0. 1 O. l 0.1 0 dry 3.0 3.1 3.1 2.4 3.2 2.8 2.9 3.2 '1. wet.-. 2.3 2.2 2.4 1.5 2.4 1.9 2.1 2.2 E. dry- 20 22 20 23 21 19 20 21 E. wet 27 28 28 29 27 23 26 26 Percent skin 100 100 100 100 100 100 100 85 Norn.-Adduct in viscose oi:

Examples I and II, 9 ethylene oxide units/molecule triethanolamine.

Examples 111 and IV, 15 ethylene oxide units/molecule triethanolamine.

Examples V and VI, 30 ethylene oxide units/molecule triethanolamine.

Addnct in bath of Examples I through V11, 9 ethylene oxide units/molecule triethanolamine.

'1. dry and T. wet-Tensile strength of dry and wet yarn, respectively, in grams per denier.

i E]. dry and E. wet-Percent elongation of dry and wet yarn, respect ve y.

The individual filaments formed in accordance with this invention have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. 1500X). The filaments of the control yarn formed from the same viscose and spun under the same conditions but in the absence of an adduct or modifier of the type described exhibit a very irregular and serrated surface and are composed of about skin and the balance core with a sharp line of demarkation between the sldn and core.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin' structure and possess improvided abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The alkylene oxide adducts of triethanolamine may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adduct may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A micro tome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few momen s each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. In a method of producing shaped bodies of regen erated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose into an aqueous spinning bath in the presence of a polyoxyalkylene glycol ether of triethanolamine containing at least about 9 alkylene oxide units per molecule of triethanolamine, the bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%, the glycol ether being present in an amount of from about 0.5% to about 4%, based upon the weight of the cellulose in the viscose when present in the viscose and from about 0.03% to about 0.5%, based on the weight of the spinning bath, when present in the spinning bath.

2. The step in the method as defined in claim 1 wherein the ether is a polyoxyethylene glycol ether of triethanolamine, containing between 9 and 30 ethylene oxide units per molecule of" triethanolamine.

3. 111 2 method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.5 to about 4%, based on the weight of the cellulose, of a polyoxyalkylene. glycol ether, of triethanolamine containing at least about 9 alkylene oxide units per molecule of triethanolamine, into an aqueous spinning bath containing from about to 25% sodium sulfate, from about 3% to zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point butnot exceeding about 8.5% V

' 4. The step in the method as defined in claim 3 wherein the ether is a polyoxyethylene glycol ether of tri- 8. The methodof-producing shaped bodies of regenerated celluloseconsisting entirely ofskinwhichcomethanolamine containing between 9 and 30 ethylene oxide units per molecule of triethanolamine.

5. In a method of producing shaped bodies of regena erated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate, from about 0.03% to about 0.5 of a polyoxyalkylene glycol ether of triethanolamine containing at least about 9 alkylene oxide units per molecule of triethanolamine and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%.

6. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 0.5% to about 4% of a polyalkylene glycol ether of triethanolamine containing at least about 9 alkylene oxide units per molecule of triethanolamine, the amount being based upon the weight of the cellulose, and extruding the viscose into an aqueous spinning bath containing from about 10% to 25 sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 8.5%.

7. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 0.5% to about 4% of a polyoxyethylene glycol ether of triethanolamine containing between about 9 and about 30 ethylene oxide units per molecule oftriethanolamine, the amount being based upon the weight of the cellulose, ripening the viscose to a sodium chloride salt point of not less than 7 and extruding the viscose into an aqueous spinning bath containing from about 16% to 20% sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 8.5%.

prises forming an aqueous spinning bath containing in solution from about 10% to sodium sulfate, from about 3% to 15% zinc sulfate, frornabout 0.03% to about 0.5% of a polyoxyalkylene glycol ether of triethanolaminecontaining at least about 9 alkylene oxide units per molecule of triethanolamine and sulfuric acid, and extruding viscose into the spinning bath, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 8.5%.

9. The method as defined in claim 8 wherein the ether is a polyoxyethylene glycol ether containing between about 9 and about ethylene oxide units per molecule of triethanolamine. V V

' 10. A viscose spinning solution containing from about 0.5% to about 4% of a polyoxyalkylene glycol ether of triethanolamine containing at least about 9 alkylene oxide units per molecule of triethanolamine, the amount being based on the weight of the cellulose in the viscose.

11. A viscose spinning'solution containing from about 0.5% to about 4% of a polyoxyethylene glycol ether of triethanolamine containing between about 9 and about 30 ethylene oxide units per molecule of triethanolamine, the amount being based on the weight of the cellulose in the viscose. I

12. An aqueous spinning bath for the production of all skin regenerated cellulose products from viscose containing from about 10% to 25% sodium sulfate, from about 3% to 15 zinc sulfate, sulfuric acid in an amount not more than about 8.5% and from about 0.03% to about 0.5 of a polyoxyalkylene glycol ether of triethanolamine containing at least about 9 alkylene oxide units per molecule of triethanolamine.

' 13. An aqueous spinning bath as defined in claim 12 wherein the ether is a polyoxyethylene glycol ether of triethanolamine containing between about 9 and about 30 ethylene oxide units per molecule of triethanolamine.

References Cited in the file of this patent UNITED STATES PATENTS 2,312,152 Davis Feb. 23, 1943 2,373,712 Schlosser Apr. 17, 1945 2,535,044 Cox Dec. 26, 1950 2,535,045 Cox Dec. 26, 1950 2,572,217 Thurmond Oct. 13, 1951 2,593,466 MacLaurin Apr. 22, 1952 2,664,360 Charles et al. Dec. 29, 1953 2,710,861 Charles et al. June 14, 1955 2,732,279 Tachikawa Jan. 24, 1956 2,775,505 Pedlow Dec. 25, 1956 2,777,775 Edwards June 15, 1957 FOREIGN PATENTS 379,760 Great Britain Aug. 25, 1932 lurk 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VICOSE INTO AN AQUEOUS SPINNING BATH IN THE PRESENCE OF A POLYOXYALKYLENE GLYCOL ETHER OF TRIETHANOLAMINE CONTAINING AL LEAST ABOUT 9 ALKYLENE OXIDE UNITS PER MOLECULE OF TRIETHANANOLAMINE, THE BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 8.5%, THE GLYCOL ETHER BEING PRESENT IN AN AMOUNT OF FROM ABOUT 0.5% TO ABOUT 4%, BASED UPON THE WEIGHT OF THE CELLULOSE IN THE VICOSE WHEN PRESENT IN THE VICOSE AND FROM ABOUT 0.03% TO ABOUT 0.5% BASED ON THE WEIGHT OF THE SPINNING BATH, WHEN PRESENT IN THE SPINNING BATH. 